(i) Field of the Invention
The present invention relates to a method and system for estimating a visceral fat area. More specifically, it relates to a method and system for estimating a visceral fat area of a subject based on height and fat mass of the subject.
(ii) Description of the Related Art
In recent years, accumulation of visceral fat has been receiving attention as a factor which exerts a significant influence on health and causes the onset of lifestyle-related disease. One method for estimating visceral fat area is by means of X-ray CT. However, to practice this method, the assistance of a radiological technician is essential due to the use of X-rays. This prevents the method from being widely used. Further, this method is disadvantageous in that it requires the subject to be exposed to X-rays. In addition, operation costs are excessively high.
There is a correlation between abdominal circumference on a navel and visceral fat area, and there is a method for estimating visceral fat area by use of the correlation. However, a measurement value of abdominal circumference on the navel is significantly influenced by where the circumference is measured, the degree of tension in the abdomen, the timing of the measurement, i.e., before or after a meal, and the condition of the subject, such as the position of the subject. Therefore, when visceral fat area is to be estimated based on only this measurement value or with emphasis on this measurement value, the estimation is liable to be influenced by the above measurement conditions. Further, when a subject tries to measure abdominal circumference on a navel by himself/herself, the subject is liable to tense his/her abdomen at the time of the measurement or make the measurement at an improper position.
In order to resolve such weak points in the known methods as mentioned above, one of the present inventors have invented a method and system for estimating the visceral fat area of a subject by using certain equation(s) which takes height, weight, fat mass and age of the subject as parameters, and filed as Japanese Patent Application No. 2001-212790 (Japanese Patent Publication No. 2003-24303) and U.S. patent application Ser. No. 10/193,281. However, it has been found in subsequent research of the present inventors that errors often occur in estimation of visceral fat area of a tall subject using these equation(s), because fat mass is directly used as an explanation variable in the equation(s), even if it includes a correction term of height.
FIG. 18A shows a correlation graph between fat mass measured using the well known Bioelectrical Impedance Analysis (hereinafter referred to as the “BIA”) in the horizontal axis and visceral fat area measured using X-ray CT in the vertical axis. Measured data of numbers of subjects are plotted in the graph; in particular the measured data of tall subjects over 180 cm are plotted as ▪ mark. The line in the graph means an equation for estimating visceral fat area using the parameter of fat mass as an explanation variable, which is acquired from the measured data. In case of the tall subjects, visceral fat area estimated using the equation is far different from the same fat area measured by using X-ray CT.
FIG. 18B shows a correlation graph between body fat percentage measured using the BIA in the horizontal axis and visceral fat area measured using X-ray CT in the vertical axis. The line in the graph represents an equation for estimating visceral fat area using a parameter of body fat percentage as an explanation variable. In case of the tall subjects, visceral fat area estimated by using this equation is far different from the same fat area measured by using the X-ray CT.
Estimation errors for tall subjects may prevent a plurality of nations, each having a different average height, from using a common equation for estimating visceral fat area. Therefore, it is necessary to prepare methods and systems for estimating visceral fat area for each nation, thereby increasing the costs of development and manufacturing.